Found 2 old AR pre-ban uppers that won’t fit any of my lowers

Quote:

---

Originally Posted by Ed L.

Here is a photo of the HBAR upper on a 6940 lower. I used a DPMS Offset Pivot Pin Adapter Bushing .315" to .250" Diameter. Even though there is no massive wiggle in the front, however if you look at the rear where the arrow is, there is a noticeable gap between the Colt AR15A2 HBAR upper and the Colt 6940 lower. It is more apparent in person than I am able to depict with my photo.

I'm not one of those people who think the upper and lower need to be super tight, but if you were to look at the gap in person, you could imagine lubrication and other things squirting out when the gun is fired.

http://i73.photobucket.com/albums/i2...ps57a559b6.jpg

---

I'm no expert, but it looks like Colt definitely changed things over the years.

To do anything remotely useful with that upper, you are going to need to track down the correct H-Bar lower for it. Could be a neat scavenger hunt project.

Just a thought, but the rear take down hole on an upper is slotted, and the front takedown hole has an eccentric/offset bushing that can rotate (at least on your setup). I'm suggesting that if the front adapter was rotated into a slightly different position, it might close up that gap.

That being said, I'd just get a new small pin upper, swap the parts and be done with it.

Thanks, guys.

I picked up a complete Colt SP-1 lower. Both uppers fit it, but with quite a bit of looseness and there seems to be a visible space between the back of the SP-1 upper and the buffer area of the SP-1 lower. This is the case with both the A1 and A2 uppers.

It has been a long time since I handled an SP1 or an M16A1. I remember the upper lower fit being loose with those, but I can't remember if it was this loose. In comparison, the fit between my Colt 6920 and 6940 is much tighter, as is the fit between those newer Colt lowers and my BCM upper as well as my 2 HK416 uppers. I guess I will have to carefully test it and find out.

Quote:

---

Originally Posted by Ed L.

Thanks, guys.

I picked up a complete Colt SP-1 lower. Both uppers fit it, but with quite a bit of looseness and there seems to be a visible space between the back of the SP-1 upper and the buffer area of the SP-1 lower. This is the case with both the A1 and A2 uppers.

---

Are you still using an adapter or do you have the correct big screw?

The SP-1 lower that I bought has the correct screw size for the front/pivot pin. It uses a pivot screw that screws into a bushing that has a screw on its face. Below is a picture of it:

http://i73.photobucket.com/albums/i2...ps9766e023.jpg

As I said in a previous post, it has been over 20 years since I last handled an SP-1 and I remember the upper/lower fit being loose, but not this loose. Here is a closeup of the upper/lower fit. If you look at the back of the upper where it mates with the buffer area of the SP-1 lower it would seem that there is a gap. Does this gap look excessive to anyone?

thanks.

http://i73.photobucket.com/albums/i2...ps112c91dc.jpg

Looks correct to me. If you dont like the play in it, then grap a disposable ear plug and place it under the rear pin which will stiffen it up. It may help if you could give a year of manufacture on that lower so we could tell if its was when colt was about to change their tooling to the SPII style which started around mid 81-82 when they started their sear block era and big trigger pins. Just ask more question you have on it if you do.

Thanks ClassIIIGunsmith ,

The lower's serial number is 1608**. The upper was part of an SP-1 bought in the fall of 1980.

I'll try and pull some of my old Colts and take pictures of the same area for comparison this week. Doesn't look too bad.

Thanks.

Maybe I'm imagining things since I have not handled an SP1 in such a long time,